Since other therapeutic modalities failed to significantly improve the overall survival of "curable" patients with colorectal cancer and that of Dukes C class in particular, we propose a long-term, carefully randomized and controlled clinical trial of adjuvant immunotherapy with BCG versus Corynebacterium parvum. This is based on a growing body of evidence that immunological parameters play a major role in the host- tumor relationship and in the natural defense against neoplasia. Our proposal derives from extensive evidence of experimental immunotherapy in animal models, from early human trials in leukemia, and solid tumors, and from our own encouraging experience in melanoma during the past 16 months. It is anticipated that adjuvant immunotherapy, given to a distinct group of patients will prolong their disease-free interval and survival, and will lead to an unprecedented milestone in the control of a major public health problem.